Examination is being made of the social/spatial organization of freely growing, confined populations of house mice. Mathematical and statistical techniques are utilized to analyze group structure in time and space. Particular emphasis is placed upon determining those factors that are related to social group development during the early phases of population growth. It is essential to know if early changes in the characteristics of social/spatial organization are related to the cessation of reproduction and eventual decline to extinction of high density populations. For example, in one population the social organization collapsed from a somewhat territorially organized society consisting of several individually identifiable groups into a single, homogeneously distributed group: there was a reduction in reproduction following the social collapse that may have led to the eventual decline and extinction of the population.